一、连词一般是单词或者词组，他们的主要作用是将文章中的内容是组合到一起。这些连词需要使用逗号与文章中的其他内容分隔开。

我们通常将逗号放在一个短语或者是副词之后，作用是为了引导出一个句子。

例如：

In addition， many disabled people suffer discrimination at work.

On the other hand, the unemployment rate has fallen.

Finally, local councils need to consider the cost of recycling schemes.

Unfortunately, there were no more tickets available.

Similarly, animals kept out doors are also vulnerable to infection.

二、某些特定单词和词组通常出现在句子的中间，在这些单词或词组的前后，我们需要使用逗号来分隔：

This problem can’t, however, be solved quite so simply.

There are more jobs in the city, but, of course, the cost of living is higher.

Which option you choose depends, to a certain extent, on your budget.

Water is particularly scarce in arid regions, for example/ for instance, in Africa.

People who live in cold countries, such as/ like Norway, have to spend more on heating.

三、在副词用于修饰限定形容词的时候，是不需要加逗号的

This was matched by a similarly dramatic increase in May.

However careful you are, accidents can always happen.